The present invention relates to a circuit arrangement for determining the polarity of the load current in a reversible d-c controller or chopper having a bridge circuit which is connected across a supply voltage source, the bridge circuit comprising four bridge arms, each of which contains an antiparallel circuit comprising an electronic switch and a bypass diode. Two bypass circuits are each formed from the two bridge arms respectively connected to the same supply bus. A measuring sensor is provided in each of two diagonal bridge arms, and the electronic switches are controlled so that the load current circulates in successive bypass periods in an alternating pattern in the two bypass circuits.
Such a circuit arrangement is known, for instance, from the journal "Elektrie" 28 (1974), pages 368 to 370. In the known circuit arrangement, resistors which are connected to the bus with reference potential are provided as measuring sensors in two bridge arms. Although this cirucit arrangement can be used to determine the magnitude and polarity of the load current at zero potential, elaborate and expensive electronic circuitry is required for evaluating the signals obtained by the measuring sensors.
An object of the invention is to provide a circuit arrangement of the type mentioned above by which the polarity of the load current can be determined in a relatively simple and convenient manner.